Otitis media (OM) ranks first in the list of the thirty most common diagnoses requiring a physician's office visit, and over one billion dollars is spent annually on treatment of this disease. It is estimated that 83% of all children will have had at least one episode of acute disease by three years of age. Nontypable strains of Haemophilus influenzae (NTHi) are significant OM pathogens and account for 25-30% of all cases of OM, 53% of recurrent OM, and are the primary pathogens isolated from 62% of cases of OME. The long-term objectives of our program are to contribute to the delineation of the pathogenic mechanisms involved in NTHi-induced OM and to develop a scientific rationale for the design of novel diagnostic, prevention, and management strategies for OM. The major hypotheses to be tested regarding the role of NTHi in OM pathogenesis are: 1) to initiate OM, NTHi must be able to colonize the nasopharynx by means of adherence to complimentary host receptors and gain access to the middle ear space; and 2) bacterial cell envelope products (eg. endotoxin) trapped in the middle ear after resolution of the acute inflammatory phase may sustain inflammation in the tubotympanum after the viable microbes have been eliminated. The specific aims for this renewal application are: 1) to further characterize fimbriae produced by NTHi and the adherence that they mediate and begin to assess the level of conservation of the gene(s) involved in their expression; and 2) to further characterize the role of endotoxin in the pathogenesis of OM and to investigate the mechanism(s) involved in endotoxin-induced epithelial cell proliferation.